The invention relates to a system comprising a housing and an electric cable, in which system:
the housing comprises an electromagnetic interference (hereinafter xe2x80x9cEMCxe2x80x9d) shielding wall with an edge,
a recess being provided at the edge in the wall, and
the wall is provided with contact means for electrically contacting the electric cable and the wall at least adjacent the recess.
The invention also relates to a housing and to an electric cable.
Such a system is known from DE 297 02 513 U1. In the known system, the contact means are at the same time means by which a fastening of the electric cable to the housing is realized. The contact means are for this purpose constructed as a clamping strap. A disadvantage of the known system is that the existence of a mechanical load on the known fastening at the same time implies that the electrical contacting is fully and directly mechanically loaded. This involves a comparatively high risk of the contacting between the electric cable and the wall being broken. Another disadvantage of the known system is that the creation of the fastening between the electric cable and the housing by means of a clamping strap is a comparatively labor-intensive and difficult process.
The contact means of the known system require comparatively much space. This is disadvantageous for an application of this system in a comparatively small chamber. Resilient tags are provided in the known system for counteracting this disadvantage to a certain extent. However, this leads to another disadvantage of the system, i.e. that the EMC shielding wall provides a less effective EMC shielding.
It is important in a number of applications that the EMC shielding wall should be safe to touch. That means that electrically conducting parts of the wall and the contact means cannot be inadvertently touched. The known system has the disadvantage that the risk of inadvertent touching is comparatively great because the contact means project comparatively far outward in the known system.
The invention has for its object to counteract the above disadvantages. According to the invention, this object is achieved in that a system of the kind described in the opening paragraph is characterized in that the electric cable comprises a fastening element, and in that a receiving element mating with the fastening element is provided on the wall, shifted relative to the recess along an axis perpendicular to the wall, into which receiving element the cable and the fastening element can be introduced from a transverse direction.
In the system according to the invention, the functions of electrically contacting the electric cable and of accommodating a mechanical (tensile) load have been partly separated. The separation in part of said functions has the advantage that the full and direct mechanical load on the electrical contacting is absent in the case of a mechanical load on the electric cable. The transverse accommodation of the fastening element counteracts an axial displacement of the cable relative to the wall, which might occur as a result of the mechanical load, in a simple manner. The mechanical load is partly accommodated by the receiving element and the fastening element. The recess may be chosen such that the cable introduced therein is held with clamping force. In that case, not only the receiving element and the fastening element, but also the recess will absorb any mechanical load which will be present. Since the mechanical load is shared among the recess, the receiving element, and the fastening element, the risk of breaking of the electrical contact in the case of mechanical loads is comparatively small.
Since the receiving element and the fastening element have corresponding shapes, the system is simple to assemble. In addition, the recess can be covered at least substantially entirely by the fastening element. This gives the system the advantage that an improved shielding of components present in the housing is obtained as compared with the known system, for example against dirt particles. The contacting can be screened off by the fastening against inadvertent touching because the contacting is provided in a direction which is axially shifted with respect to the fastening. The advantage of this is that the system has become safer to touch.
Finally, the system in which the electrical contacting and accommodation of the mechanical loads have been realized in the manner described has the advantage that the system is comparatively compact.
In an embodiment of the system, the receiving element is an integral portion of the wall. The receiving element and the wall may thus be manufactured from one piece and in one and the same operation, for example by injection molding. Preferably, the receiving element comprises a second wall which is at least substantially parallel to the wall and is situated at least at the area of the recess, and a space between the wall and said second wall. The wall is thus a double wall at the area of the recess. The two walls have respective recesses which are axially displaced relative to one another. A compact system for cord anchorage and electrical contacting is achieved in a simple manner in that the fastening element is given a shape by which it can be accommodated in the space and hooks itself behind the second wall.
In an alternative embodiment of the system, the recess has an inner surface, while the contact means are chosen from the group formed by an electrically conducting resilient portion at the inner surface or axially displaced relative to the inner surface on the wall, an electrically conducting cutting contact at the inner surface or axially displaced relative to the inner surface on the wall, and an electrically conducting layer on the inner surface. The system has become even safer to touch because the contacting is concealed in or behind the wall. In addition, a yet more compact system is achieved thereby.
In a favorable embodiment of the system, the recess has a tapering shape in a transverse direction from the edge. A cable introduced into the tapering recess will be clamped therein automatically. No additional components are required for fastening the cable to the housing in this case. Provided the electric cable remains pressed home under a permanent pressure in the direction in which the recess tapers, for example by means of a lid which closes off the recess at least partly, the cable will automatically remain clamped in in the recess. If the contact means in addition comprise a cutting contact, they will cut themselves into the electric cable while the latter is being introduced into the recess. The electrical contacting may thus be achieved without separate operations being necessary for it. Because of the permanent clamping force on the cable there is an enhanced risk on a permanent deformation of the cable and, on a result, there is a risk on an impaired contracting during lifetime. If the electric cable has a sheath for the purpose of contacting the contact means, a metal bush may be provided directly below the sheath at the area where the cable is passed through the recess so as to counteract permanent deformation of the cable. The risk of an impaired contacting between the electric cable and the housing in the course of product life is improved thereby.
In a preferred embodiment of the system, the fastening element is an integral portion of the electric cable. The cable and the fastening element may thus be readily manufactured in one and the same operation, for example through injection molding. The system can thus be manufactured comparatively inexpensively.
In another favorable embodiment of the system, the fastening element has a U-shaped cross-section in transverse direction. This U-shaped cross-section counteracts a mechanical loading of the contacting or of portions of the electric cable present inside the housing owing to, for example, torsion of the cable relative to the housing. The risk of the cable becoming detached, with the resulting short-circuit in the system, is reduced thereby. The system has thus become more robust and safer.
An embodiment of the system is characterized in that the fastening element comprises metal and/or is provided with an electrically conducting layer. Such a fastening system ensures that comparatively small EMC leaks in the EMC shielding wall adjacent the recess are eliminated. It is achieved in a very simple manner thereby that the EMC shielding by the wall is yet further improved.
The EMC shielding wall may in its entirety consist of metal, for example of cast aluminum, but it may alternatively be manufactured from a synthetic resin, for example PVC or polyethylene, which is provided with an electrically conducting layer, for example of aluminum or copper. The layer may be present outside or inside the housing. If the layer is provided inside the housing, the housing is suitable for an application in which it should be safe to touch.
The electric cable may have several electrically conducting core wires of which at least one is designed for the electrical contacting with the wall. Alternatively, the cable may have a core wire which is surrounded by an electrically conducting sheath which is not in electrical connection with the core wire for the purpose of EMC shielding, for example a coaxial cable.